This invention relates to an apparatus and method for welding a stack of laminations to form a stator. The invention also relates to a nest tool used to hold a stack of stator laminations in position for processing and welding.
A stator of an electric motor is typically formed by welding a series of metal plates, known as laminations, together to form the stator. To facilitate the welding process, the laminations are usually carried in a stacked arrangement on a carrier and welded together to form the stator while remaining on the carrier. In the prior art, the laminations are stacked on a carrier having pins which pass through holes in the laminations to align the laminations for welding. These pins are usually no larger than one-eighth of an inch in diameter and, because of their small diameter, are easily bent during the welding process.
Stator laminations, when machined, have burrs, can be oily and stick together. Typically, the laminations are stamped from sheet metal. Often, the thickness of laminations will vary depending upon the portion of the sheet metal from which they are stamped. Usually, laminations cut from the same area of the sheet metal will vary in thickness from the side of the lamination that is stamped from the portion of sheet metal near the center of the sheet to the side of the lamination stamped from the portion of the sheet metal near the edge of the sheet. Manufacturing specifications for laminations typically allow a variation in thickness for each lamination of .+-.0.003 inch. As the number of laminations in a stack of laminations increases, the variation in thickness of the single laminations can cause the stack of laminations to lean to one side. Further, because of this thickness variation, providing a stack of laminations by a count of the number of laminations may result in stators having non-uniform size.
To manufacture the stator, a stack of laminations is welded along its sides. To ensure that the stack of laminations is properly welded, the stack must be tightly clamped so that no gaps exist between the laminations. As one can imagine, a weld can not be properly formed on the stack of laminations if spaces exist between the laminations. Previously in the art, a stack of laminations would be moved into position in a welding apparatus and, in the welding apparatus, the stack of laminations would first be clamped to prevent gaps from forming between the individual laminations. Once the laminations had been clamped, the clamped stack of laminations would be moved upwardly in the welding apparatus past stationary welding torches to weld the laminations. The clamping mechanism included an arbor which performed the functions of clamping the stack and aligning the laminations. The stack of laminations had to be maintained in a constant, clamped condition to ensure proper welding.
The prior art method of moving a stack of clamped laminations past stationary welding torches caused stress on the welding apparatus which resulted in excessive wear of the parts of the apparatus. The force required to maintain the stack of laminations in a clamped condition as the stack was moved past the welding torches damaged the arbor and clamping mechanism. Further damage to the apparatus resulted when welding stacks having a nonuniform size, the welding torches often welded portions of the welding apparatus other than the stack of laminations by starting at a position higher than the stack and/or ending at a position lower than the stack.